CN108414113B - Fire alarm system and method for predicting optical fiber temperature with multi-point temperature dispersion coefficient - Google Patents

Abstract

The invention discloses a fire alarm system and a method for predicting the temperature of an optical fiber by using a multipoint temperature dispersion coefficient.A distributed optical fiber temperature measurement system is used for acquiring the light intensity values of Anti-Stokes light and Stokes light at each point of the optical fiber and the corresponding demodulated temperature value, processing the acquired light intensity and temperature value, and comparing the temperature and light intensity with an alarm threshold value to determine whether a differential temperature or constant temperature alarm condition is met; meanwhile, the temperature at the next moment is predicted by using the current temperature value and the discrete coefficients of the temperatures at a plurality of past points, and whether an alarm is needed or not is judged; if the alarm condition is met, the alarm position is positioned, and the alarm time is displayed. The method introduces a light intensity judgment method in the differential temperature alarm method, thereby effectively reducing the probability of false alarm; in the method for prejudging the temperature of the optical fiber, the temperature change condition at the future moment is predicted by using the discrete coefficients of the current temperature and the past temperature, so that the alarm response time is effectively reduced.

Description

Fire alarm system and method for predicting optical fiber temperature with multi-point temperature dispersion coefficient

technical field

The invention relates to the technical field of temperature detection, in particular to a fire alarm system and method for predicting the temperature of an optical fiber by using a multi-point temperature dispersion coefficient.

Background technique

The distributed optical fiber Raman temperature measurement system mainly uses the principle of spontaneous Raman scattering in the optical fiber to measure the temperature, and uses the principle of optical time domain reflection to locate, and realizes a new temperature sensing system for real-time measurement of the temperature field. Compared with traditional electronic temperature sensors, it has inherent characteristics and intrinsic safety such as electrical insulation, corrosion resistance, geometric structure variability, wide signal transmission bandwidth, and low long-distance transmission loss of information. It is widely used in the detection of oil wells, oil depots and pipelines, seismic survey observation, monitoring of power systems and communication systems.

In the temperature alarm method of the distributed Raman temperature measurement system, the current mainstream alarm method is to set a fixed alarm threshold when the system is started. Start the alarm. The speed of this alarm method mainly depends on the acquisition rate of the high-speed acquisition card and the running time of the temperature demodulation program. It is demanding, uneconomical and does not guarantee accuracy. In some places with high requirements for temperature early warning, such as underground safety, forest fire prevention, aerospace and other temperature measurement places, such temperature alarm methods with slow response time and single early warning method cannot be safe and accurate.

Since the existing temperature alarm methods for distributed Raman temperature measurement are limited by the acquisition speed of the acquisition card, they cannot meet the national security standards in these places where accurate alarms are required, and new temperature alarm methods with faster response are urgently needed to adapt to these Temperature measurement needs in major places.

In addition, the application number of the existing patent document is "201710095023.9", and the patent name is "Intelligent temperature early warning method for Raman thermometers". The algorithm of the optical fiber temperature prediction program used is complex and cannot meet the needs of timely fire alarm.

SUMMARY OF THE INVENTION

In order to solve the deficiencies of the prior art, the present invention provides a fire alarm system that uses the multi-point temperature dispersion coefficient to predict the temperature of the optical fiber, and solves the problem that the temperature alarm method of the existing distributed optical fiber temperature measurement system has a slow response time and cannot be accurately and effectively predicted. temperature issue.

Fire alarm systems that use multi-point temperature dispersion coefficients to predict the temperature of optical fibers, including: distributed optical fiber Raman temperature measurement systems,

The light intensity values of Stokes light and anti-Stokes light at each point of the fiber, as well as the corresponding demodulated temperature values, are collected through the distributed optical fiber temperature measurement system, and the collected light intensity and temperature values are processed. By comparing the temperature and light intensity with the alarm threshold, it is determined whether the differential temperature or constant temperature alarm conditions are met; at the same time, the current temperature value and the dispersion coefficient of the temperature at several points in the past are used to predict the temperature at the next moment;

During temperature prediction, measure and record the previously set sub _{-temperature data at the current time T n at} the same position of the optical fiber in a continuous period of time. Average value, if the absolute value of the difference between the average temperature of the third group and the average temperature of the second group is greater than the absolute value of the difference between the average temperature of the third group and the average temperature of the second group, then the second Temperature prediction alarm, otherwise, set the threshold value of dispersion coefficient difference, and calculate the absolute value of the difference between the multi-point temperature dispersion coefficient at the current time and the multi-point temperature dispersion coefficient at the previous time in the previously set sub-temperature data of the current time T _n , if If the absolute value is greater than the threshold value of the set dispersion coefficient difference, the first temperature prediction alarm is performed.

Further, the distributed fiber Raman temperature measurement system includes a pulsed laser, and the pulsed light emitted by the pulsed laser enters the reference fiber through a wavelength division multiplexer, and then enters the sensing fiber through an optical switch;

In the middle part of each sensing fiber, two lengths of fibers with a certain length are randomly selected as the first reference fiber and the second reference fiber, and are respectively placed in the corresponding constant temperature water bath equipment.

Further, the pulsed light generates backscattered light at each point inside the reference fiber and the sensing fiber, wherein the backward Stokes light and the backward anti-Stokes light pass through two of the wavelength division multiplexer. The output end enters the photodetector, and then collects the calculation and AD conversion through the high-speed acquisition card, and obtains the light intensity curve of the Stokes light and the anti-Stokes light. The light intensity curve demodulates the temperature information distributed along the fiber, that is, the temperature-position curve distributed along the fiber.

Further, the input end of the wavelength division multiplexer is connected to the pulsed laser, the common end of the wavelength division multiplexer is connected to the reference fiber, and the two output ends of the wavelength division multiplexer output Stokes light and anti-Stokes light respectively. The light is sent to the two input ends of the photoelectric detector, and the two output ends of the photoelectric detector are connected to the high-speed acquisition card, which is transmitted to the main board through acquisition and conversion, and then demodulates the temperature information.

Further, the optical switch is a four-channel optical switch, which controls the opening and closing of the four channels, the common end of the optical switch is connected to the reference fiber, and the four channels are respectively connected to four long-distance sensing fibers.

Further, the power supply provides power for the above-mentioned pulsed laser, optical switch, photodetector, high-speed acquisition card and mainboard.

Further, the reference fiber is a silica fiber with a length of about 150 meters.

The present application also discloses a fire alarm method for predicting the temperature of an optical fiber with a multi-point temperature dispersion coefficient, including:

The first reference fiber is placed in the first constant temperature water bath device, and the temperature is set to T ₁ , the second reference fiber is placed in the second constant temperature water bath device, and the temperature is set to T ₂ ;

Start the distributed optical fiber Raman temperature measurement system. The distributed optical fiber Raman temperature measurement system demodulates the temperature information distributed along the optical fiber through the light intensity curves of Stokes light and anti-Stokes light, and draws the temperature- position curve;

Set the constant temperature alarm threshold, differential temperature alarm threshold, start the temperature demodulation program, start the constant temperature alarm program, the differential temperature alarm program and the temperature prediction program;

If it is detected that the temperature value of a certain position of the optical fiber is greater than the fixed temperature alarm threshold, the alarm program will start, the alarm indicator light will be on, the system will locate the alarm position and display the alarm time;

If it is detected that the difference between the current temperature of a certain position of the optical fiber and the previous moment is greater than the alarm threshold of the difference temperature in a continuous period of time, the alarm program starts, the alarm indicator light is on, and the system locates the alarm position and displays the alarm time;

Temperature prediction program: measure and record the previously set sub _{-temperature data of the current time T n at} the same position of the optical fiber in a continuous period of time. Average value, if the absolute value of the difference between the average temperature of the third group and the average temperature of the second group is greater than the absolute value of the difference between the average temperature of the third group and the average temperature of the second group, then the second Temperature prediction alarm, otherwise, set the threshold value of dispersion coefficient difference, and calculate the absolute value of the difference between the multi-point temperature dispersion coefficient at the current time and the multi-point temperature dispersion coefficient at the previous time in the previously set sub-temperature data of the current time T _n , so If the absolute value is greater than the threshold value of the set dispersion coefficient difference, the first temperature prediction alarm is performed.

Further, the temperature demodulation formula of the distributed optical fiber Raman temperature measurement system is as follows:

in

In the formula, P _AS and P _S represent the optical power of the backward anti-Stokes Raman scattered light and the backward Stokes Raman scattered light, respectively, υ is the propagation speed of the light in the fiber, and E ₀ is the pump The energy of the laser pulse, h and κ are the Planck constant and Boltzmann constant, respectively, Δυ is the Raman frequency shift in the silica fiber, Γ _AS and Γ _S are the backward reaction per unit length in the fiber, respectively. Scattering coefficients of Stokes Raman scattered light and backward Stokes Raman scattered light, α ₀ , α _AS , α _S are the incident pump light (backward Rayleigh scattered light), the backward inverse The loss coefficient of the Tox Raman scattered light and the backward Stokes Raman scattered light per unit length in the fiber, L is the distance from a measurement point on the corresponding fiber to the measurement starting point, and T is the measurement point The absolute temperature, T ₀ is a certain set temperature.

Further, when calculating the absolute value of the difference between the multi-point temperature dispersion coefficient at the current time and the multi-point temperature dispersion coefficient at the previous time in the previously set sub-temperature data at the current time T _n , the multi-point temperature dispersion coefficient at the previous time is the previous one. The ratio of the standard deviation of the multi-point temperature at the moment to the average value of the multi-point temperature at the previous moment, the multi-point temperature dispersion coefficient at the current moment is added to the current moment temperature T _{n during the calculation, and the data with the farthest time from the current moment temperature T n is} excluded, The multi-point temperature dispersion coefficient at the current time is the ratio of the standard deviation of the multi-point temperature at the current time to the average value of the multi-point temperature at the current time.

Further, the differential temperature alarm procedure: firstly check whether the temperature value satisfies the condition 1, if the condition 1 is satisfied, then start to check the condition 2, if the condition 1 and the condition 2 are satisfied at the same time, the alarm will alarm;

Among them, condition 1: if it is detected that the difference between the current temperature of a certain position of the optical fiber and the change of the previous moment in a continuous time is greater than the difference temperature alarm threshold;

Condition 2: Calculate the light intensity corresponding to the temperature difference to obtain _PL , continuously record the light intensity values P ₁ and P _{2 of the optical fiber at the same position at the previous moment and the next moment, and} calculate the light intensity difference P _d =|P ₁ /c ₁ -P ₂ /c ₂ |, if P _d ≥ P _L , where c ₁ and c ₂ are the position-related dynamic coefficients of the optical fiber at the same position at the previous moment and the next moment, respectively.

Further, the difference threshold of the dispersion coefficient is set according to the setting of different constant temperature alarm thresholds combined with the results of repeated experiments.

Compared with the prior art, the beneficial effects of the present invention are:

The all-fiber temperature prediction method of the present invention is a method of predicting future temperature changes by using the latest temperature data obtained. For a new temperature data, the data with the farthest time from the current moment is removed from the original set data to ensure the real-time and accurate prediction results. The algorithm of this application has a small complexity and a faster calculation time. Can meet the requirements of fire alarm.

Compared with the existing alarm methods applied to distributed optical fiber temperature measurement, the method has three temperature alarm methods: constant temperature alarm method, differential temperature alarm method and temperature prediction method, and the light intensity is introduced into the differential temperature alarm method. The judgment method effectively reduces the probability of false alarms compared with the existing alarm methods that only rely on the temperature change rate; in the optical fiber temperature prediction method, the dispersion coefficient of the current temperature and the past temperature is used to judge and predict the temperature change in the future. situation, effectively reducing the alarm response time.

The light intensity reference is introduced into the differential temperature alarm method of this application to reduce the probability of false alarms; the algorithm used in the temperature prediction method makes it meet the alarm time requirement of the national standard.

The present application adds a method of detecting the temperature at multiple points to determine the temperature at the next moment, so that it is not necessary to wait until the time point when the acquisition card collects and calculates to reach the threshold temperature to predict whether an alarm is required.

In this method, the method of light intensity judgment is introduced into the differential temperature alarm method, which effectively reduces the probability of false alarm; in the pre-judgment method of optical fiber temperature, the discrete coefficient of the current temperature and the past temperature is used to predict the temperature change in the future, effectively reduces the alarm response time.

Description of drawings

The accompanying drawings that constitute a part of the present application are used to provide further understanding of the present application, and the schematic embodiments and descriptions of the present application are used to explain the present application and do not constitute an improper limitation of the present application.

Fig. 1 is the structure diagram of the distributed optical fiber Raman temperature measuring system in the invention;

Fig. 2 is the flow chart of the temperature alarm procedure of the distributed optical fiber Raman temperature measuring system in the invention;

In the picture: 1-pulse laser, 2-WDM, 3-reference fiber, 4-optical switch, 5-APD, 6-high-speed acquisition card, 7-mainboard, 8-power supply.

Detailed ways

It should be noted that the following detailed description is exemplary and intended to provide further explanation of the application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

It should be noted that the terminology used herein is for the purpose of describing specific embodiments only, and is not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly dictates otherwise, the singular is intended to include the plural as well, furthermore, it is to be understood that when the terms "comprising" and/or "including" are used in this specification, it indicates that There are features, steps, operations, devices, components and/or combinations thereof.

In a typical embodiment of the present application, as shown in FIG. 1 , a fire alarm system for predicting the temperature of an optical fiber by using a multi-point temperature dispersion coefficient is provided, including: a distributed Raman temperature measurement system, including a pulsed laser (1), WDM (2), reference fiber (3), optical switch (4), APD (5), high-speed acquisition card (6), mainboard (7), power supply (8), first constant temperature water bath equipment, second constant temperature water bath equipment , sensing fiber.

The pulse laser (1) includes a pulse generator, a seed source laser, a pump laser, a temperature control module, a WDM1, an erbium-doped fiber, a WDM2, and an optical filter.

Among them, WDM1 and WDM2 are located inside the pulsed laser, which is 1x2WDM; WDM(2) is located in the system outside the light source, which is 1x3WDM; the wavelengths passed are different.

The input end of the WDM (2) is connected to the pulsed laser (1), the common end is connected to the reference fiber (3), and the two output ends respectively output Stokes light and anti-Stokes light to the two input ends of the APD (5). , the two outputs of the APD (5) are connected to the high-speed acquisition card (6), and are transmitted to the main board (7) through acquisition and conversion, and then the temperature information is demodulated

The reference fiber (3) is a silica fiber with a length of about 150 meters;

The optical switch (4) is a four-channel optical switch, which controls the opening and closing of the four channels, the common end is connected to the reference fiber (3), and the four channels are respectively connected to four long-distance sensing fibers.

The power supply (8) supplies power to the pulsed laser (1), the optical switch (4), the APD (5), the high-speed acquisition card (6) and the main board (7).

In another typical embodiment of the present application, a specific fire alarm method for predicting the temperature of an optical fiber with a multi-point temperature dispersion coefficient is disclosed, including:

Step 1: Based on the above-built fire alarm system for predicting the temperature of the optical fiber with the multi-point temperature dispersion coefficient;

Step 2: The middle parts of the four sensing fibers are randomly selected as the first and second reference fibers with two lengths of fibers. The first reference fiber is placed in the first constant temperature water bath equipment, and the temperature is set to a constant temperature of 20 °C. The reference fiber is placed in the second constant temperature water bath, and the temperature is set to 20°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 84°C, 91°C, 98°C at different times (inside the constant temperature water bath) The filling liquid is edible oil).

Step 3: As shown in Figure 2, start the distributed fiber Raman temperature measurement system. The pulsed light from the pulsed laser passes through the WDM, enters the reference fiber, and then enters the sensing fiber through the optical switch. The pulsed light is in the reference fiber and the sensing fiber. Backscattered light occurs at each point in the interior, in which the backward Stokes light and the backward anti-Stokes light enter the APD through the two output ends of the WDM, and then collect and calculate through the high-speed acquisition card, AD conversion, and get the Stokes light. Light intensity curves of Stokes light and anti-Stokes light;

Step 4: The Raman temperature measurement system demodulates the temperature information distributed along the fiber through the light intensity curves of Stokes light and anti-Stokes light, and draws a temperature-position curve;

The specific temperature demodulation formula is as follows:

in

In the formula, P _AS and P _S represent the optical power of the backward anti-Stokes Raman scattered light and the backward Stokes Raman scattered light, respectively, υ is the propagation speed of the light in the fiber, and E ₀ is the pump The energy of the laser pulse, h and κ are the Planck constant and Boltzmann constant, respectively, Δυ is the Raman frequency shift in the silica fiber, Γ _AS and Γ _S are the backward reaction per unit length in the fiber, respectively. Scattering coefficients of Stokes Raman scattered light and backward Stokes Raman scattered light, α ₀ , α _AS , α _S are the incident pump light (backward Rayleigh scattered light), the backward inverse The loss coefficient of the Tox Raman scattered light and the backward Stokes Raman scattered light per unit length in the fiber, L is the distance from a measurement point on the corresponding fiber to the measurement starting point, and T is the measurement point The absolute temperature, T ₀ is a certain set temperature.

In this experiment, the temperature of the second constant temperature water bath equipment is divided into 10 groups of experiments. °C, 98 °C.

Set the system operating temperature as _Ta . The differential temperature alarm threshold is T _b ;

Constant temperature alarm program: Take the temperature of the second constant temperature water bath equipment as 84℃ as an example, if the current temperature value of a certain position of the optical fiber is greater than 60℃ after demodulation, the alarm program will be started, the alarm indicator will be on, and the system will display the alarm time and alarm position;

Differential temperature alarm program: Condition 1: If it is detected that the difference between the current temperature of the fiber at a certain position and the previous moment is greater than T _b in continuous time; Condition 2: Calculate the light intensity corresponding to the temperature difference T _b to obtain _PL , and record the same position continuously The light intensity values P ₁ and P ₂ at the previous moment and the next moment of the optical fiber, calculate the light intensity difference P _d =|P ₁ /c ₁ -P ₂ /c ₂ |, if P _d ≥ P _L , where c ₁ , c ₂ is the position-related dynamic coefficient of the fiber at the same position at the previous moment and the next moment, respectively.

First, check whether the temperature value satisfies condition 1. If condition 1 is met, start checking condition 2. If condition 2 is met at the same time, enter differential temperature alarm procedure 2, and the alarm will alarm;

Temperature prediction program: measure and record the first 15 temperature data of the current time T _n at the same position of the fiber in a continuous time, and record them as T _n-15 , T _n-14 , T _n-13 ,...,T _n-2 ,T _n-1 ;

Calculate T _n1 =(T _n-11 +T _n-12 +T _n-13 +T _n-14 +T _n-15 )/5,

T _n2 =(T _n-6 +T _n-7 +T _n-8 +T _n-9 +T _n-10 )/5,

T _n3 =(T _n-1 +T _n-2 +T _n-3 +T _n-4 +T _n-5 )/5;

Compare the values of T _n1 , T _n2 , and T _n3 in turn, if |T _n3 -T _n2 |≥|T _n2 -T _n1 | and display the alarm time; otherwise, enter the prediction procedure ₁ : according to the constant temperature alarm threshold T1, set the threshold of the dispersion coefficient difference as _cv ,

Calculate the discrete coefficients of the 15 points T _n-15 , T _n-14 , T _n-13 ,..., T _n-2 , T _n-1 , and the specific calculation method is c _v1 =σ ₁ /μ ₁ ,

where μ ₁ =(T _n-15 +T _n-14 +T _n-13 +...+T _n-2 +T _n-1 )/15,

Add the temperature T _n at the current moment, remove T _n-15 , calculate the discrete coefficients of the 15 points T _n-14 , T _n-13 , ..., T _n-2 , T _n-1 , T _n , and calculate the specific The method is c _v2 =σ ₂ /μ ₂ ,

where μ ₂ =(T _n-14 +T _n-13 +...+T _n-2 +T _n-1 +T _n )/15,

Calculate _Δ c _v =|c _v1 -c _v2 |, if _Δ c _v >c _v ,

Then start the alarm program, the alarm indicator light is on, the system locates the alarm position and displays the alarm time.

Among them, _cv is set according to different constant temperature alarm thresholds, temperature alarm and discrete coefficient correlation theory and the results of repeated experiments.

After the alarm ends, restart the temperature demodulation program and the temperature alarm program, and restart the temperature demodulation and temperature prediction.

The invention collects the light intensity values of the Anti-Stokes light and Stokes light at each point of the fiber, and the corresponding demodulated temperature values through a distributed optical fiber temperature measurement system, and processes the collected light intensity and temperature values, and then processes the collected light intensity and temperature values. Compare with the light intensity and the alarm threshold to determine whether the differential temperature or constant temperature alarm conditions are met; at the same time, use the current temperature value and the dispersion coefficient of the temperature at several points in the past to predict the temperature at the next moment, and determine whether an alarm is required; if the alarm conditions are met, Then locate the alarm position and display the alarm time. In this method, the method of light intensity judgment is introduced into the differential temperature alarm method, which effectively reduces the probability of false alarm; in the pre-judgment method of optical fiber temperature, the discrete coefficient of the current temperature and the past temperature is used to predict the temperature change in the future, effectively reduces the alarm response time.

Compared with the prior art, under the same hardware conditions, the present invention can perform temperature early warning faster; according to the regulations in GB-16280-2014, at the initial temperature of 25°C ± 2°C (for the setting action Under the condition that the temperature is not less than 138℃, the initial temperature is 50℃±2℃) and the airflow rate is 0.8m/s±0.1m/s, for the sensitive parts of any standard alarm length of the detector, the rate is 1℃/min The corresponding time of the constant temperature and differential constant temperature detector should meet: the detector operating temperature is 60≤T≤85℃, and the alarm time is not more than 15 seconds.

In this method, we have determined the thresholds of the discrete coefficients corresponding to different operating temperatures through a large number of repeated experiments, and can accurately determine whether the An alarm is required, which has obvious advantages in fire alarming compared with the existing methods.

The above descriptions are only preferred embodiments of the present application, and are not intended to limit the present application. For those skilled in the art, the present application may have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of this application shall be included within the protection scope of this application.

Claims (9)

1. A fire alarm system for predicting the temperature of an optical fiber by using multipoint temperature discrete coefficients is characterized by comprising the following components: a distributed optical fiber Raman temperature measuring system is provided,

collecting light intensity values of Stokes light and anti-Stokes light of each point of the optical fiber and corresponding demodulated temperature values through a distributed optical fiber temperature measuring system, processing the collected light intensity and temperature values, and comparing the temperature and light intensity with an alarm threshold value to determine whether a differential temperature or constant temperature alarm condition is met;

during temperature prediction, the current time T of the same position of the optical fiber is measured and recorded in continuous time_nThe previous setting of the secondary temperature data, the current time T_nDividing the previously set secondary temperature data into three groups according to the time sequence, averaging the temperature data of each group, if the absolute value of the difference between the temperature average value of the third group and the temperature average value of the second group is larger than the absolute value of the difference between the temperature average value of the second group and the temperature average value of the first group, performing second temperature prediction alarm, otherwise, setting a threshold value of the difference of discrete coefficients, and calculating the current time T_nIf the absolute value of the difference between the multipoint temperature discrete coefficient at the current moment and the multipoint temperature discrete coefficient at the previous moment in the previously set secondary temperature data is greater than the threshold value of the set discrete coefficient difference, a first temperature prediction alarm is carried out;

and (3) a differential temperature alarm program: firstly, detecting whether the temperature value meets a first condition, if so, starting to detect a second condition, and if so, alarming by an alarm;

wherein, the difference temperature alarm program: the first condition is as follows: if the difference value of the current temperature of a certain position of the optical fiber and the change of the previous moment in the continuous time is detected to be greater than T_b(ii) a And a second condition: calculating the temperature difference T_bThe corresponding light intensity is obtained as P_LContinuously recording the light intensity values P of the optical fiber at the same position at the previous moment and the next moment₁、P₂Calculating the light intensity difference P_d＝|P₁/c₁-P₂/c₂If P_d≥P_LWherein c is₁，c₂Are dynamic coefficients related to the position of the optical fiber at the same position at the previous moment and the next moment respectively.

2. The fire alarm system using the multipoint temperature dispersion coefficient to predict the temperature of the optical fiber according to claim 1, wherein the distributed fiber Raman temperature measurement system comprises a pulse laser, and pulse light emitted by the pulse laser enters the reference optical fiber through a wavelength division multiplexer and then enters the sensing optical fiber through an optical switch;

the middle part of each sensing optical fiber is respectively and randomly selected to be used as a first reference optical fiber and a second reference optical fiber with a certain length, and the two optical fibers are respectively placed in the respective corresponding constant-temperature water bath equipment.

3. The fire alarm system using the multi-point temperature dispersion coefficient to predict the fiber temperature according to claim 2, wherein the pulse light generates backward scattered light at each point inside the reference fiber and the sensing fiber, wherein the backward stokes light and the backward anti-stokes light enter the photoelectric detector through two output ends of the wavelength division multiplexer, then the light intensity curves of the stokes light and the anti-stokes light are obtained through the acquisition operation and the AD conversion of the high-speed acquisition card, and the temperature information distributed along the fiber, that is, the temperature-position curve distributed along the fiber is demodulated through the light intensity curves of the stokes light and the anti-stokes light.

4. The fire alarm system according to claim 2, wherein the input terminal of the wavelength division multiplexer is connected to the pulse laser, the common terminal of the wavelength division multiplexer is connected to the reference fiber, two output terminals of the wavelength division multiplexer respectively output stokes light and anti-stokes light to two input terminals of the photodetector, and two output terminals of the photodetector are connected to the high-speed acquisition card and transmitted to the main board through acquisition and conversion to demodulate the temperature information.

5. The fire alarm system according to claim 2, wherein the optical switch is a four-channel optical switch for controlling the opening and closing of four channels, the common end of the optical switch is connected to the reference optical fiber, and the four channels are respectively connected to the four long-distance sensing optical fibers.

6. The fire alarm method for predicting the optical fiber temperature by using the multipoint temperature discrete coefficient is characterized by comprising the following steps:

the first reference optical fiber is placed in first constant-temperature water bath equipment, and the temperature is set to be T₁The second reference optical fiber is placed in a second constant-temperature water bath device, and the temperature is set to be T₂；

Starting the distributed fiber Raman temperature measurement system, demodulating temperature information distributed along the fiber by the distributed fiber Raman temperature measurement system through the light intensity curves of Stokes light and anti-Stokes light, and drawing a temperature-position curve;

setting a constant temperature alarm threshold value and a differential temperature alarm threshold value, starting a constant temperature alarm program, a differential temperature alarm program and a temperature prediction program while starting a temperature demodulation program;

if the temperature value of a certain position of the optical fiber is detected to be larger than the constant temperature alarm threshold value, an alarm program is started, an alarm indicator lamp is turned on, and the system positions the alarm position and displays the alarm time;

if the difference value between the current temperature and the previous moment at a certain position of the optical fiber in the continuous time is detected to be greater than the differential temperature alarm threshold value, an alarm program is started, an alarm indicator lamp is turned on, and the system positions the alarm position and displays the alarm time;

temperature prediction procedure: measuring and recording the current time T of the same position of the optical fiber in continuous time_nThe previous setting of the secondary temperature data, the current time T_nDividing the previously set secondary temperature data into three groups according to the time sequence, averaging the temperature data of each group, if the absolute value of the difference between the temperature average value of the third group and the temperature average value of the second group is larger than the absolute value of the difference between the temperature average value of the second group and the temperature average value of the first group, performing second temperature prediction alarm, otherwise, setting a threshold value of the difference of discrete coefficients, and calculating the current time T_nThe absolute value of the difference between the multipoint temperature dispersion coefficient at the current time and the multipoint temperature dispersion coefficient at the previous time in the previously set secondary temperature data is larger than the threshold of the set dispersion coefficient difference, and then the first temperature is carried outPredicting and alarming;

wherein, the difference temperature alarm program: firstly, detecting whether the temperature value meets a first condition, if so, starting to detect a second condition, and if so, alarming by an alarm;

wherein, the condition one: if the change difference value of the current temperature and the previous moment of a certain position of the optical fiber in the continuous time is detected to be larger than the differential temperature alarm threshold value;

and a second condition: calculating the light intensity corresponding to the temperature difference value to obtain P_LContinuously recording the light intensity values P of the optical fiber at the same position at the previous moment and the next moment₁、P₂Calculating the light intensity difference P_d＝|P₁/c₁-P₂/c₂If P_d≥P_LWherein c is₁，c₂Are dynamic coefficients related to the position of the optical fiber at the same position at the previous moment and the next moment respectively.

7. The method of claim 6, wherein the distributed fiber Raman temperature measurement system has a temperature demodulation formula as follows:

wherein

In the formula, P_AS、P_SRespectively representing the optical power of backward anti-Stokes Raman scattered light and backward Stokes Raman scattered light, upsilon is the propagation speed of light in the optical fiber, and E₀H and k are respectively Planck constant and Boltzmann constant, Delnu is Raman frequency shift quantity in quartz optical fiber, and gamma is energy of pumping light pulse_AS、Γ_SScattering coefficients of backward anti-Stokes Raman scattered light and backward Stokes Raman scattered light per unit length in an optical fiber, respectively, α₀、α_AS、α_SRespectively are loss coefficients of incident pump light, backward anti-Stokes Raman scattered light and backward Stokes Raman scattered light in a single unit length of an optical fiber, L is the distance from a certain measuring point on the corresponding optical fiber to a measuring starting point, T is the absolute temperature of the measuring point, and₀is a certain temperature set.

8. The fire alarm method of claim 6, wherein the current time T is calculated_nWhen the absolute value of the difference between the current-time multipoint temperature dispersion coefficient and the previous-time multipoint temperature dispersion coefficient in the previously set secondary temperature data is obtained, the previous-time multipoint temperature dispersion coefficient is the ratio of the standard deviation of the previous-time multipoint temperature to the average value of the previous-time multipoint temperature, and the current-time multipoint temperature dispersion coefficient is added to the current-time temperature T during calculation_nRejecting the temperature T at the current moment_nAnd in the data of the farthest time, the current-time multipoint temperature dispersion coefficient is the ratio of the standard deviation of the current-time multipoint temperature to the average value of the current-time multipoint temperature.

9. The method of claim 6, wherein the discrete coefficient difference threshold c is a multiple of the discrete coefficient difference threshold c_vThe method is set according to the result of setting different constant temperature alarm thresholds and combining multiple repeated experiments.

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